The present invention relates to a novel tryptoanthorine derivative and an electrophotosensitive material which is used for image forming apparatuses such as copying apparatus and laser beam printer.
In the image forming apparatuses such as copying apparatus, an organic photosensitive material such as an organic photoconductor (OPC) having a sensitivity within the wavelength range of a light source of the apparatus has exclusively been used.
As the organic photoconductor, a multi-layer type photoconductor comprising an electric charge generating layer and an electric charge transferring layer, which are mutually laminated, is well known, but a single-layer type photoconductor wherein an electric charge generating material and an electric charge transferring material are dispersed in the same layer is also known.
Although a high carrier mobility are required to the electric charge transferring material to be used for these photoconductors, almost all of electric charge transferring materials having a high carrier mobility are hole transferring materials having hole transferring properties and, therefore, only negative charging type multi-layer type organic photoconductors, which are provided with an electric charge transferring layer at their outer layer from the viewpoint of mechanical strength, are used for practical application. However, since the negative charging type organic photoconductor utilizes negative-polarity corona discharge, problems such as large amount of ozone generated, environmental pollution, deterioration of photosensitive material, etc. have arisen.
Accordingly, in order to eliminate the above drawbacks, it has been studied to use an electron transferring material as the electric charge transferring material. In Japanese Unexamined Patent Publication No. 1-206349, there is suggested that a compound having a diphenoquinone structure is used as the electron transferring material for electrophotosensitive material.
However, it is difficult for electron transferring materials such as diphenoquinones to match with the electric charge generating material, which results in insufficient injection of electrons from the electric charge generating material into electron transferring material. Therefore, sufficient photosensitivity could not be obtained.
Furthermore, if the single-layer and dispersion type organic photoconductor can be used, a lot of advantages can be obtained, e.g. easy production of the photoconductor, prevention of coat failure, improvement of optical characteristics, etc. However, the single-layer type organic photosensitive layer had a problem that the electron transfer is inhibited by an interaction between diphenoquinone and an hole transferring material.
On the other hand, in Japanese Unexamined Patent Publication No. 4-295853, there is suggested that an electrophotosensitive material having a high sensitivity is made by the combination of an electron transferring material of 3,5-dimethyl-3',5'-di-t-butyl-4,4'-diphenoquinone, a hole transferring material of alkyl substituted triphenyldiamine, etc., and an electric charge generating material of a phthalocyanine pigment. However, the resulting photosensitive material is insufficient in wear resistance.
Furthermore, in Japanese Unexamiend Patent Publication No. 61-134354, there is disclosed a 3,3'-dimethylbenzidine derivative as a compound having a high hole transferring capability. However, this derivative normally has a low melting point (about 180.degree. C. or less) and, therefore, the photosensitive layer obtained using the derivative has a low glass transition temperature, and durability and heat resistance of the photosensitive material are insufficient.
Furthermore, regarding the polarity of the photosensitive material to be charged, the scope of application of the photosensitive material can be widen if one photosensitive material can be used for both positive charging and negative charging types. However, such a photosensitive material has never been put into practice.